This invention relates generally to the measurement and study of optical phenomena which occur at very high repetition rates and which have a time duration in the picosecond or sub-picosecond range. The invention is particularly concerned with electron-optical image tube systems for use in obtaining a record of pulses generated from a laser, and also with streak cameras operating with a time resolution of the picosecond or sub-picosecond range and capable of providing direct linear measurement of such ultra-short pulses.
My U.S. Pat. No. 3,973,117 describes an electron-optical image tube system which is particularly suited for use with a continuous wave mode-locked laser and which enables a direct linear intensity profile of the average pulse of a pulse train to be obtained.
The image tube system described in the aforesaid patent specification comprises a photocathode for receiving repetitive pulse-form light images and converting them to pulses of photoelectrons, an extraction electrode immediately adjacent to the emission side of the photocathode to accelerate the photoelectrons away from the photocathode and project them into a path on the output side of the extraction electrode at increased velocity, deflection electrodes on the path of the photoelectrons beyond the extraction electrode, means defining an aperture beyond said deflection electrodes on which the photoelectrons are arranged to impinge, the deflection electrodes being arranged to cause the electrons to follow a path at the aperture-defining means having a rotational component of motion about the longitudinal axis of the tube, control means adjustable so that the photoelectron pulses may be caused to coincide with the aperture, and detector means on the side of the aperture remote from the electrodes to receive photoelectrons passing through the aperture.
The means defining the aperture may be a plate positioned on the axis of the tube and perpendicular to the axis, with one or more slits therethrough disposed along radii of the tube.
When used with a source of ultra-short light pulses the known system may include phase control means to control the phase of the voltage applied to the deflection electrodes to produce a circular or spiral deflection path on the means defining the aperture.